Re: [PATCH 5/5] drm/bridge: samsung-dsim: calculate porches in Hz

[Adam Ford]

On Mon, Aug 28, 2023 at 10:59 AM Michael Tretter
<m.tretter@xxxxxxxxxxxxxx> wrote:
>
> Calculating the byte_clk in kHz is imprecise for a hs_clock of 55687500
> Hz, which may be used with a pixel clock of 74.25 MHz with mode
> 1920x1080-30.
>
> Fix the calculation by using HZ instead of kHZ.
>
> This requires to change the type to u64 to prevent overflows of the
> integer type.
>
I would argue this needs a fixes tag since the previous calculations
were not accurately generated for many resolutions and refresh rates.

Reviewed-by: Adam Ford <aford173@xxxxxxxxx>  #imx8mm-beacon
Tested-by: Adam Ford <aford173@xxxxxxxxx>  #imx8mm-beacon

> Signed-off-by: Michael Tretter <m.tretter@xxxxxxxxxxxxxx>
> ---
>  drivers/gpu/drm/bridge/samsung-dsim.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index 459be953be55..eb7aca2b9ab7 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -973,10 +973,12 @@ static void samsung_dsim_set_display_mode(struct samsung_dsim *dsi)
>         u32 reg;
>
>         if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> -               int byte_clk_khz = dsi->hs_clock / 1000 / 8;
> -               int hfp = DIV_ROUND_UP((m->hsync_start - m->hdisplay) * byte_clk_khz, m->clock);
> -               int hbp = DIV_ROUND_UP((m->htotal - m->hsync_end) * byte_clk_khz, m->clock);
> -               int hsa = DIV_ROUND_UP((m->hsync_end - m->hsync_start) * byte_clk_khz, m->clock);
> +               u64 byte_clk = dsi->hs_clock / 8;
> +               u64 pix_clk = m->clock * 1000;
> +
> +               int hfp = DIV64_U64_ROUND_UP((m->hsync_start - m->hdisplay) * byte_clk, pix_clk);
> +               int hbp = DIV64_U64_ROUND_UP((m->htotal - m->hsync_end) * byte_clk, pix_clk);
> +               int hsa = DIV64_U64_ROUND_UP((m->hsync_end - m->hsync_start) * byte_clk, pix_clk);
>
>                 /* remove packet overhead when possible */
>                 hfp = max(hfp - 6, 0);
>
> --
> 2.39.2
>